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  <a href="http://sudopedia.enjoysudoku.com/ALS-XY-Wing.html">ALS-XY-Wing</a>
  <p>
   Almost Locked Sets (ALS) are groups of N cells in a single house with N+1 candidates (e.g. 3 cells with 4 candidates).<br> 
   The three cell groups <b>{0} (ALS A)</b>, <b>{1} (ALS B)</b> and <b>{2} (ALS C)</b> are all <a href="http://sudopedia.enjoysudoku.com/Almost_Locked_Set.html">Almost Locked Sets</a>.
  </p>
  <p>
   <b>Digit {6}</b> is <a href="http://sudopedia.enjoysudoku.com/Restricted_common.html">restricted common</a>
    to the two ALSes A and B meaning it cannot be present in both sets at the same time.<br/>
  </p>
  <p>
   <b>Digit {7}</b> is <a href="http://sudopedia.enjoysudoku.com/Restricted_common.html">restricted common</a>
    to the two ALSes B and C meaning it cannot be present in both sets at the same time.<br/>
  </p>
  <p>
   ALS A and C have the <b>common candidate {8}</b>. One of the ALSes has to contain that common candidate. Here's why:<br>
   <ul>
    <li>f ALS A doesn't contain <b>{8}</b>, then it has to contain <b>{6}</b> (minus one candidate makes it a locked set).</li>
    <li>If ALS A contains <b>{6}</b>, then ALS B cannot contain <b>{6}</b> because that's their restricted common. Digit <b>{7}</b> gets therefore locked into ALS B.</li>
    <li>If ALS B contains <b>{7}</b>, then ALS C cannot contain <b>{7}</b> because that's their restricted common. Digit <b>{8}</b> gets therefore locked into ALS C.</li>
   </ul>
   The same argumentation also works in opposite direction: if ALS C doesn't contain <b>{8}</b>, ALS A must. 
  </p>
   Because either ALS A or ALS C contain <b>digit {8}</b>, none of the cells seeing all these ALS cells can contain <b>digit {8}</b> as a candidate.
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